Port Forwarding.
SO, the next step is to set up port forwarding. This will enable your router to correctly send incoming information to the server, and allow other users to connect. Again, it seems daunting, until you know how to do it.
You’ll need to access your router settings. How you go about this depends on the makeand modelof your router.
Once you’ve done this, you’ll be taken to your router setting home screen. And, it will ask you to log in with a name and password. To further complicate matters, you’ll need admin privileges. I can’t help you here, except to say that if nobody has changed the default admin account, you can probably Google your router brand to find out what the default settings are.
This is a great place for a disclaimer: If you don’t own the router, or pay the internet bill, you should probably seek the permission of the person who does before changing then router settings.
Second disclaimer: If you have a dynamic IP address (the IP changes periodically through a range of addresses), you’ll need a service such as noip.com to set up port forwarding. My IP is static, and I’ve not mastered noir. Perhaps someone such as Bibliophile could explain it?
So, we’ve accessed the router settings, and logged on to the admin account. Things get a little dicey from here, as no two router brands seem to be set up exactly the same, though most are pretty similar. The router screen should have a 'Basic" tab, and an ‘Advanced’ tab. go to the advanced tab, and look for 'Advanced Settings" (or something along those lines. We’re looking for the tab labeled “port forwarding”:
Now, look for the button marked ‘Add Service’, ‘Add new Service’, ‘Add Custom Service’, etc… It should prompt you for the following information:

Service name: You can use most anything here. I normally make it the same as the server name.
Service type: UDP. Always. so far as i know, it won’t work otherwise
External starting and ending port: The port you’re going to use. For our example it’s 15152
You’ll notice I have the ‘Use same port range for internal port’ box checked, so it fills in automatically as i type in the fields above.
Internal IP Address: Every device connected to the router has a unique internal IP address. Use the address for the device that has the Blockhead Server App installed. (in my case, my Macbook Air)
Click OK, Apply, or whatever your router uses.
Thats it. You should get an overview of what you just typed in:
The only thing left is to see if you can connect to the server, as well as someone else outside your home (to make sure forwarding is set up correctly)
I’ve only recently figured out all this for myself, but if you have questions, i’ll do my best.